Such bus systems are made up of a control device having a multicore line—in this case a two-wire design, in particular—to which devices such as, for example, up to 30 items having different functions but sharing a uniform interface are connected. In a two-wire bus system, the line, which is made up of only two wires, is used for different purposes simultaneously. For one, electrical energy for the supply of the connected devices is transmitted via the bus line and, for another, the bus line transmits data to the connected devices and from there to the control device.
Such a bus system is used in different application areas, for instance in the manufacturing industry, in households, motor vehicles, and many other places, and is exposed to a multitude of electrical and electromagnetic influences in the process. For instance, these influences generate so-called transients in the bus system, i.e., specific electrical pulses that have different amplitudes and frequencies and may influence the bus system in different ways by causing interference and malfunctions.
To protect against these transients, diodes, which shortcircuit these transients and thus prevent further damage to the devices, are utilized in each device connected to the bus, for instance. If irradiation of high-frequency electromagnetic effects occurs, it will be demodulated by the diodes. This produces a d.c. voltage on the bus line, which superimposes itself on the transmission voltages on the bus line and thus may cause interference. To reduce this effect, capacitors are connected in parallel to the diodes in each connected device. However, their capacitance must not exceed a certain relatively low value since this capacitance puts a capacitive load on the bus with each connected device. The frequency range of the irradiation interference to be attenuated is restricted as a result. The suppressing effect of such a capacitor through its capacitive resistance, which is inversely proportional to the frequency and capacitance, thus sets in at high frequencies only.